1. Field of the Invention
The invention relates to techniques for obtaining an image from nuclear magnetic resonance (NMR) data. More specifically, the invention relates to techniques for applying pulses to an object to obtain a series of NMR echoes, which may then be processed and transformed, such as by a Fourier transform, to obtain an image.
2. Description of the Prior Art
The application of the Fourier transform to NMR imaging was demonstrated by A. Kumar, D. Welti, and R. R. Ernst. "NMR Fourier Zeugmatography", Journal of Magnetic Resonance 18 (1975), pp. 69-83. U.S. Pat. No. 4,070,611, issued Jan. 24, 1978 to R. R. Ernst, is related to that article and discloses a technique for NMR Fourier imaging in which a series of measurements are taken, each based on a single "Free Induction Decay" signal (FID). The sampled FID's are then stored and processed to obtain an image. The processing includes the use of a computational algorithm approximating the Fourier transform, such as the "Fast Fourier Transform" (FFT). The process may also include arranging a series of FID's, each FID being obtained separately.
U.S. Pat. No. 4,290,019, issued Sept. 19, 1981 to J. M. S. Hutchison et al., discloses another technique for NMR Fourier imaging. This technique includes the application of a sequence of gradient fields and high frequency pulses to obtain a spin echo of the FID. After an echo is obtained, the atoms being imaged are permitted to relax before the sequence is repeated to obtain another echo. The echoes are processed to obtain an image, and the processing includes Fourier transformation.
Other NMR Fourier imaging techniques have been proposed. For example, U.S. Pat. No. 4,319,190, issued Mar. 9, 1982 to T. R. Brown, discloses a technique in which the FID is sampled and stored for subsequent transformation to obtain a chemical shift image.
These prior art NMR Fourier imaging techniques have demonstrated that Fourier imaging can be applied to NMR data. It would be advantageous, however, to provide NMR Fourier imaging techniques which would produce images with improved contrast. In addition, it would be advantageous to provide NMR Fourier imaging techniques in which the data acquisition times are shortened, by reducing the need for additional signal averaging.